70’s era (and earlier) gear became ebay-valuable and has disappeared from the thrift/ goodwill circuit. This previously served as the entry point for a lot of audio heads and now it’s more of a BPC show.

Nah, RCA to connect pre and amp and speaker cable, which on the low end can be “lamp cord” from your hardware store.

The vendor below is a solid source for moderately-fussy/ priced cables:

https://www.bluejeanscable.com/indexmob.htm

Check pg 5-6 of the linked owner’s manual:

http://www.berners.ch/McIntosh/Downloads/C28_own.pdf